XIII 



PHYLUM CIIORDATA 



191 



Tt.Sp 



Tt.a. 



850, s, ^.) is very deep and inclined backwards; on the ventral 

 surface ot" tlie basis craaii is a pit {yi.) fur the extra-cranial purtiun 

 of the pituitary body. The posterior portion of the cranial cavity 

 is very high ; the anterior part — containing most of the fore-brain — 

 is low and tunnel-like, and has above it a cavity of almost equal 

 size {Nx. o 0.) for the ophthahnic branches of the iifth nerves. 

 The greater part of the membranous labyrinth is lodged in a 

 series of pits on the sitle-walls of the cranium {ci.s.c, p.s.c), and is 

 separated from the brain by membrane only. The occipital region 

 articulates with the verte- 

 bral column by a single 

 saddle-shaped surface or 

 condyle (oc. en.). There is a 

 great development of labial 

 cartilages, particularly 

 noticeable being a large 

 plate which, in Callorhyn- 

 clius, lies just externally to 

 the mandible, nearly equal- 

 ling it in size and having 

 the appearance of a second- 

 ary or external jaw. In 

 Callorhynchus the snout is 

 supported by three cartilagi- 

 nous rods growing forward 

 from the cranium, of which 

 one (r.) is median and dorsal 

 and repiesents the rostrum ; 

 these, as well as the great 

 lower labial are represented 

 by comparatively small 

 structures in Chima'ra (Fig. 

 M\),lh:^). 



The hyoid resembles the 

 branchial arches in form and 

 is little superior to them in 

 size. Above the epihyal 

 (Fig. 849, e. hy.) is a small 



cartilage {]ph. hy.), evidently serially homologous with the pharyngo- 

 branchials, and therefore to be considered as a 'pharyngohyal. 

 It represents the hyomandibular of Elasmobranchs, but, having 

 no function to perform in the support of the jaws, it is no 

 larger than the corresponding segments in the succeeding arches. 

 Long cartilaginous rays {o]i. r.) for the support of the operculum 

 are attached to the ceratohyal. 



The first dorsal fin is remarkable for having all its pterygio- 

 phores fused into a single plate, which articulates Avith the 



B 



n.ci 



Flu. .S4S.— Chimaera inonstrosa. A, tmusvorse 

 section i)f the vertebral culiuuii ; B, lateral view of 

 the same. r. r. calcified ring ; h. r. li;«mal ridge ; 

 iiit. intercalai-y piece ; n. a. neui-al arch ; arli. 

 liusition of notochordal tissue ; uclc .v/t. sheath of 

 notuchord ; ii. .■<p. neural sx^ine. (After Hasse.) 



